⤷ Control behind the other ones

If you have some control and want to stay this control on top of the other ones, then you may put this control in front of the other controls by using BringToFront property.
Use SendToBack property to reverse order of controls.

procedure TForm1.Button1Click(Sender: TObject);
begin
  Memo1.SendToBack;
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
  Memo1.BringToFront;
end;
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